/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.zookeeper.server.quorum;

import java.io.IOException;
import java.util.concurrent.ConcurrentLinkedQueue;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.zookeeper.server.FinalRequestProcessor;
import org.apache.zookeeper.server.Request;
import org.apache.zookeeper.server.RequestProcessor;
import org.apache.zookeeper.server.SyncRequestProcessor;
import org.apache.zookeeper.server.ZKDatabase;
import org.apache.zookeeper.server.persistence.FileTxnSnapLog;

/**
 * A ZooKeeperServer for the Observer node type. Not much is different, but we
 * anticipate specializing the request processors in the future.
 *
 */
public class ObserverZooKeeperServer extends LearnerZooKeeperServer {
	private static final Logger LOG = LoggerFactory.getLogger(ObserverZooKeeperServer.class);

	/*
	 * Request processors
	 */
	private CommitProcessor commitProcessor;
	/*
	 * Pending sync requests
	 */
	ConcurrentLinkedQueue<Request> pendingSyncs = new ConcurrentLinkedQueue<Request>();

	private SyncRequestProcessor syncProcessor;

	ObserverZooKeeperServer(FileTxnSnapLog logFactory, QuorumPeer self, DataTreeBuilder treeBuilder, ZKDatabase zkDb)
			throws IOException {
		super(logFactory, self.tickTime, self.minSessionTimeout, self.maxSessionTimeout, treeBuilder, zkDb, self);
	}

	/**
	 * Unlike a Follower, which sees a full request only during the PROPOSAL phase,
	 * Observers get all the data required with the INFORM packet. This method
	 * commits a request that has been unpacked by from an INFORM received from the
	 * Leader.
	 * 
	 * @param request
	 */
	public void commitRequest(Request request) {
		commitProcessor.commit(request);
	}

	@Override
	public Learner getLearner() {
		return self.observer;
	}

	public Observer getObserver() {
		return self.observer;
	}

	@Override
	public String getState() {
		return "observer";
	}

	/**
	 * Set up the request processors for an Observer:
	 * firstProcesor->commitProcessor->finalProcessor
	 */
	@Override
	protected void setupRequestProcessors() {
		// We might consider changing the processor behaviour of
		// Observers to, for example, remove the disk sync requirements.
		// Currently, they behave almost exactly the same as followers.
		RequestProcessor finalProcessor = new FinalRequestProcessor(this);
		commitProcessor = new CommitProcessor(finalProcessor, Long.toString(getServerId()), true);
		commitProcessor.start();
		firstProcessor = new ObserverRequestProcessor(this, commitProcessor);
		((ObserverRequestProcessor) firstProcessor).start();
		syncProcessor = new SyncRequestProcessor(this, new SendAckRequestProcessor(getObserver()));
		syncProcessor.start();
	}

	/*
	 * Process a sync request
	 */
	synchronized public void sync() {
		if (pendingSyncs.size() == 0) {
			LOG.warn("Not expecting a sync.");
			return;
		}

		Request r = pendingSyncs.remove();
		commitProcessor.commit(r);
	};
}
